Portable storage devices such USB memory, a memory stick, an SD memory card, an external hard disk and the like are widely used in a computer, a cellular phone, a camera or the like.
Although such a portable storage device stores private information such as a security certificate or the like in many cases, the private information is easy to be leaked out by loss or the like of the device, and thus security setting is particularly required. Generally, the security setting is accomplished in a method of individually setting a password for a data or using separate security software.
Security process on a data is accomplished through encryption and decryption, and a secret key cryptographic algorithm and a public key cryptographic algorithm are widely used for the security process. The secret key cryptographic algorithm is a method of using the same key for encryption and decryption, and a transmitter and a receiver should safely exchange the key before performing a secure communication. A public key cryptographic algorithm is developed to relieve such an inconvenience. However, since the public key cryptographic algorithm takes a long processing time and its implementation is complicated, the secret key cryptographic algorithm attracts attention again in recent days when encryption speed is gradually considered as being important.
Although a method using a password is widely used as an authentication method in the security setting, this is unsafe since the password can be lost or exposed to other people, and particularly, it needs to further strengthen security of a portable storage device having excellent portability, such as USB memory or the like.